Mhlnews 2703 F 35 Jet Fighter

AGVs Help Jet Fighters Fly Off the Line

May 8, 2012
Lockheed Martin recruited a special breed of guided vehicle to enable precision assembly of a fighter plane a day. The right stuff means not only being automated, but autonomous

The F-35 Joint Strike Fighter (JSF) owes a bit of its existence to Henry Ford. Lockheed Martin Aeronautics adapted his concepts of mass production and common parts to affordably produce this multirole aircraft for multiple branches of the U.S. military—Air Force, Navy and Marine Corps—as well as U.S. allies.

There’s not much that’s simple about this 5th generation fighter’s technology. It combines stealth, fully fused sensor information and network-enabled operations. A portion of Lockheed Martin’s facility in Marietta, Ga., is dedicated to manufacturing the center wing section at a pace that accommodates a production rate of one aircraft a day. This production line replaces one that was first built at Lockheed Martin’s facility in Fort Worth, Tex.

With accommodations for F-35 production in Fort Worth resulting in floor space challenges, a portion of the fighter’s production was moved to Marietta. This new production line presented a material handling challenge of its own—one that couldn’t be addressed with overhead handling. The automotive industry proved to be a role model with its use of automated guided vehicles.

Why Guided Vehicles?

The Fort Worth facility’s use of overhead rail to move the wing assembly from station to station would not offer the time or space efficiency needed at the Marietta facility. The layout of the Marietta facility would require the kind of efficiency found in a car plant producing 20 to 40 vehicles an hour, so what better source to borrow material handling best practices from than the automotive industry?

“The aerospace industry has benefited from the experience of the automotive industry because its high production rates have pushed technology to be more automated,” says Peter Neumeier, of the aerospace engineer staff at Lockheed Martin. “We needed a production line to satisfy the rate of one aircraft a day for whatever variant was coming down the line. The Marietta facility had floor space constraints. So we performed a lean event and determined we needed to find a different solution to the transport of the center wing section. Fort Worth’s overhead rail system took up too much floor space and didn’t give us the flexibility we were looking for. We decided an AGV of some kind was a better solution.”

Lockheed selected Fori Automation to provide the AGV system. According to Paul Meloche, vice president of sales for Fori, much of the AGV technology implemented at Lockheed that came from the automotive industry included the components that enable production capacity and accuracy. But Fori implemented some new technologies as well.

“Our drive steer mechanism provides the steering and propulsion,” Meloche says. “It’s a suspended drive steer so it can articulate over rough concrete. We also developed a precision sensor measurement device for the magnetic field.”

No Tolerance for Variance

Precision is the key word here, since the components of the center wing section have extremely tight tolerances. Many AGVs guided by a magnetic stripe wander left or right while following the path. Fori developed a 12-inch-wide precision magnetic measuring device that gauges the intensity of the magnetic field, enabling a vehicle to position itself at an assembly station to an accuracy within 4-5 mm.

Each AGV measures 67” wide, 181” long and 28” high, and supports tooling that, combined with the center wing section, weighs about 12,000 pounds. The tooling is transported to 14 different process stations and each AGV must hold that tolerance every time it’s moved.

“We have these six pillars at each station that hold the tool in place and the tool doesn’t just sit on them, it mechanically clamps to the tool,” Neumeier explains. “So the station and the tool become one once the tool is deposited at the station. These tools also have to interact with automatic drilling machines that drill somewhere between 2000-3000 holes every time they sit in a station.”

With a tool measuring 20 ft tall, Lockheed runs the risk of deflections resulting in different tolerances at the top of the tool than at the bottom. That meant the tool and the station designs were critical, as was their interaction with the AGVs.

An AGV comes in underneath the tool and picks it up, then works through the associated safety protocols before moving the tool out of the station and into another. Each time an AGV slides under the tooling, a cup and cone arrangement clamps the AGV, which ensures a secure engagement. Accomplishing this required synchronicity among the navigation, guidance and propulsion systems as well as with the servo motors in the lifting mechanism.

Arranging Return of Investment

Three AGVs interact autonomously with two automatic drilling machine stations and 12 manual operation stations in the production line. A complete line move is accomplished on a third shift in less than six hours. Lockheed needed to ensure that by the next morning when the mechanics and technicians arrive they were looking at a new assembly in order to meet the one-a-day production rate.

Each AGV is powered by four banks of batteries. For now the plan is for these vehicles to be used once a day on third shift so each can be fully charged during 1st and 2nd shifts in preparation for the next day’s set of moves.

Fori calls these AGVs MTAVs (fot MulTitask Autonomous Vehicles). The idea is that if you dedicate an AGV to only one task it’s harder to achieve an ROI, especially in manufacturing environments with lower production rates.

“In automotive you almost have to dedicate the AGV to the application or to a specific piece of tooling,” Meloche says. “What we’ve come up with is the idea that the AGV has to do more than be dedicated to moving a single part down the line. We like to separate the part and the tooling from the AGV so maybe one or two can handle parts in multiple moves.”

For example, in a project Fori did for Bombardier, another aerospace manufacturer, in addition to moving an aircraft through assembly, AGVs go to other areas of the plant to retrieve materials and components and bring them lineside.

“We build the AGV so you can kit it and add operator platforms and lifts around the periphery of the vehicle so it becomes a moving platform,” Meloche adds.

Fori is looking at the feasibility of AGVs equipped with robots to accomplish precision drilling. Other applications could include locking two AGVs together to create an extra long, extra high capacity synchronized AGV. In the meantime, Lockheed Martin is still learning all the ins and outs of what AGVs can do.

“At the beginning people expected we’d just drop an AGV in the flow line and everything would work,” he says. “They didn’t realize there’s a period of breaking in, teething pain and experience gathering. We had Fori out a few times to modify the code to speed the process. We changed some of the safety zones to be slightly different in configuration because of potential interference.”

Lockheed finished factory acceptance testing of its AGV system in the last quarter of 2011 and has four months of production experience with the system as this is written. The transitioning of production from Fort Worth to Marietta is also in the completion phase, so Neumeier expects productivity to only get better.

Making AGVs Juicier

AIthough industrial batteries are the primary power sources for the AGVs used at Lockheed Martin, the drive toward lower cost and higher productivity is making ultracapacitors an attractive option in many industries, according to Chad Hall, vice president of sales at Ioxus, makers of these power devices. His company acquired Power Systems, which specializes in ultracapacitors for AGVs.

“A couple manufacturers of lift trucks use them and the payoff time is 1-2 years, depending on how much the operator runs the lift truck,” he says. “It makes the battery last longer per charge and gives it a two to four times increase in life. Traditionally an AGV using lead acid batteries operates six hours before a swap is needed. That can take 20-30 minutes, plus the time of traveling to the battery change station. But with an AGV you can put inductive charging in the floor under spots where the vehicle will be stopping. The ultracapacitor enables recharging more frequently, using less energy each time you recharge.”

He adds that ultracapacitors are designed for higher cycle life so could be active for 10 years before needing replacement. This is particularly important in applications that handle heavy loads over long distances. Hall claims ultracapacitors can provide hundreds or thousands of amps, and thus increase lift capabilities when used in tandem with lead acid batteries.

“For those applications a battery would perform some of the work, but the ultracapacitor would handle the major current portions of the cycle,” he explains. “You can thus increase your payload capability and incorporate regeneration. Ultracapacitors can accept a charge much faster than a battery can—seconds vs hours.”

In one plastics manufacturing facility AGVs are used to position and relocate materials throughout the plant. Ultracapacitors enable 24/7/365 operation, Hall says.

He adds that hybridization will open markets to ultracapacitor applications, citing fuel cells as a natural fit.

“The best application is to hybridize the energy store, where you use a battery or fuel cell with the ultracapacitor,” he concludes. “Fuel cells are great at producing energy but horrible at producing power. You can’t change the current output from a fuel cell without causing some damage to it.”

Latest from Technology & Automation